The present invention relates to a belt conveyance device configured so as to permit changing an endless belt.
Among belt conveyance devices are ones in which a loop-like path of movement is formed from a rotating endless belt passed over and tensioned with a plurality of tension rollers including a drive roller and an idle roller. Such a belt conveyance device is applied, for example, in an image forming apparatus utilizing the electrophotography method, to an intermediate transfer unit that conveys a full-color toner image, which is made up through a series of primarily transfers performed in such a manner that toner images of respective hues from each of a plurality of image forming sections are sequentially superimposed onto an intermediate transfer belt, to a secondary transfer position where a secondary transfer of the full-color toner image is performed onto a paper sheet, and is also applied to a secondary transfer unit including a secondary transfer belt that conveys the paper sheet to the secondary transfer position, and so forth.
In the belt conveyance device, it is important to suppress meandering of the endless belt in order to prevent the occurrence of a positional deviation of the image in relation to the paper sheet. In the case where the endless belt is passed over the drive roller and the idle roller and tensioned therewith, the meandering of the endless belt is more influenced when one end portion of the idle roller is displaced in a direction perpendicular to a conveyance direction of the endless belt between the drive roller and the idle roller than when it is displaced along the conveyance direction.
Among the conventional belt conveyance devices are ones in which in an attempt to suppress the meandering of the endless belt passed over with tension in a horizontal direction the amount of the meandering of the endless belt is detected with a sensor and then a position in the upward and downward direction of the one end portion of the idle roller tensioning the endless belt is adjusted depending on the result of the detection. As for a configuration that permits the adjustment of the position in the upward and downward direction of the one end portion of the idle roller, known is one that allows changing a rotational angle of an eccentric cam in contact with one end portion of a shaft of the idle roller from underside (for example, refer to Japanese Patent Unexamined Publication No. 10-260590 bulletin).
In the conventional belt conveyance device, however, it has been necessary to remove the eccentric cam from a main body section of the belt conveyance device whenever a replacement of the endless belt has to be made; and when the eccentric cam is removed once, the eccentric cam is not restored correctly to its original rotational angle even when it is installed again after the replacement of the belt is made; so that it can occur that the position in the upward and downward direction of the one end portion of the idle roller deviates from a state prior to the disassembly. The positional deviation in the upward and downward direction of the one end portion of the idle roller causes the endless belt to meander.
The present invention is directed to providing a belt conveyance device that permits correctly restoring a position of an idle roller in a direction perpendicular to a conveyance direction of an endless belt between a plurality of tension rollers which the endless belt is passed over and tensioned with, when a replacement of the endless belt is made.